This invention relates to interferometers used in spectral analysis instruments. It is concerned primarily with the desire to combine (a) high resolution, (b) improved alignment, and (c) easy replaceability of components.
In common assignee U.S. Pat. Nos. 4,537,508 and 4,556,316, interferometer spectrometer structures are disclosed in which one or both interferometer arms combine a retroreflector with a "folding" mirror which causes the radiation to retrace its path after it has been directed by the beamsplitter to the retroreflector. In certain embodiments, two retroreflectors are used to determine the lengths of the radiation paths in the interferometer arms, one retroreflector being movable, and the other stationary.
The "folding" effect provides a significant improvement in resolution, because a given increment of travel of the movable retroreflector produces a much greater differentiation between the lengths of the interferometer arms.
The present invention is intended to deal with certain limitations of the structures discussed above. One such limitation is sensitivity to temperature variations, which can cause misalignment in the optical system. Another limitation is the difficulty of changing beamsplitters to accommodate wavelength differences in the radiation employed in the system.